1. Field of the Invention
The present invention relates to current drive technology for a display panel having current-driven light emitting elements, such as organic EL (electroluminescence), arranged in a matrix.
2. Description of the Related Art
There is known a display device that includes a display panel having organic EL elements as self-luminous elements arranged in a matrix and drives the organic EL elements using electric current. A display device using organic EL elements is characterized by low power consumption, no illumination part, such as a backlight, and a very fast display response speed, and hence regarded as a promising future display device.
In the display device described above, a current drive circuit on the anode side of the organic EL elements (anode driver) generates a grayscale drive current according to display brightness based on a constant current. For example, the current drive circuit disclosed in Japanese Patent Application Laid-open (JP-A) No. 2003-288051 includes a current mirror circuit and uses the mirror ratio of the current mirror circuit to generate multi-grayscale drive currents.
The conventional current drive circuit includes a grayscale generation circuit (corresponding to the “D/A conversion circuit” in JP-A No. 2003-288051) that generates a current (grayscale current) according to the grayscale and an output circuit that amplifies and outputs the grayscale current. However, a smaller grayscale current results in a smaller gate-source voltage VGS in the MOSFET that is a component of the current mirror circuit in the first stage of the output circuit. Therefore, when the conventional grayscale generation circuit is used, variation in operation threshold voltage of the MOSFET likely affects the current from the output circuit (current to be supplied to an organic EL element). There has thus been a desire for a current drive circuit and a display device with smaller variation in output current and hence smaller variation in brightness of display elements.